Radar Assimilation over Kwajalein Atoll

Report No. ARL-TR-8831
Authors: Brian P Reen, Huaqing Cai, John W Raby
Date/Pages: October 2019; 54 pages
Abstract: Radar-reflectivity observations from the Kwajalein Atoll were converted into 3-D fields of latent heating temperature tendency terms (LHT) and used to replace the microphysics temperature tendency term in the Weather Research and Forecasting numerical weather prediction model for two cases on the same day. Applying LHT from a series of 15-min radar observations during a preforecast data-assimilation period substantially improved short-term reflectivity forecasts. The benefits last longer for forecasting overall coverage of reflectivity compared to forecasting placement of convection. The length that improvements in placement last vary substantially between the two cases with improvement lasting approximately 3 h for the case with stronger, more widespread convection, and improvement lasting <1 h for the other case. The radar data provide the most benefit when the data-assimilation period is longer, with 6-h assimilation periods usually performing better than 2-h and 1-h assimilation periods. Potential benefits were seen by changing the LHT to zero when the model forecasted reflectivity too high to prevent overstimulation of convection. It was not clear if adding a cooling term to more efficiently suppress erroneous convection was beneficial.
Distribution: Approved for public release
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Last Update / Reviewed: October 1, 2019